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      11-24-2020, 08:23 PM   #1
aquasurf
aquasurf
Australia
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Drives: 2016 120i
Join Date: Oct 2015
Location: Sydney

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Replacing runflat tyres and getting a suitable spare wheel

I recently bought a 2016 120i with genuine 11k km. Looks and feels like a brand new car but the Continental runflats fitted on factory 18 inch alloys were noisy. I replaced the OEM fronts 225/40R18 (on 7.5Jx18, ET+45 rims) with the nominal overall tyre diameter of 637 mm and rears 245/35R18 (on 8Jx18 ET+52 rims) with the nominal overall tyre diameter of 629 mm with four new Continental 235/40R18 tyres with the nominal overall tyre diameter of 645 mm (mere 2.5% increase against the OEM rear tyre). I note there was no problem with rubbing of the slightly wider front tyres, so no spacers were needed.

Without the runflats I needed a spare wheel. BMW specified temporary spare wheel was T125/80R17 on a 3.5x17 inch rim. As it was not readily and cheaply available, I selected instead a steel 3.5x18 inch space saver and bought a BMW temporary spare wheel (5x120 mm, centre hole diameter 74.1 mm - never used) fitted with T155/90R18 tyre that was too big for use on Series 1. It may have come from an X5 but at $50 it was cheap. I decided on T125/70R18 tyre for the spare wheel as its nominal overall tyre diameter was 633 mm, a near perfect match for the new 235 tyres (-1.9% difference). I found that such a tyre was fitted as OEM on temporary spare wheels specified for VW Golf gen 7, produced from 03/2013 till present and bought such a wheel for $100 from a local wrecker. I mounted the VW tyre on the BMW rim and my mission was accomplished.

The BMW X5 rim centre hole measuring 74.1 mm in diameter is slightly larger that the Series 1 wheel hub measuring 72.6 mm in diameter. The spare wheel can still be fitted but it is better to use a suitable hub centering ring available from on line shops (see picture below).


A new boot floor placed on top of the spare just matched the height of the boot opening, as shown in the photos. Apparently BMW had designed the boot that way on purpose.

For completeness I attached a table of BMW rim/tyre combinations specified for Series 1.
Attached Images
  

Last edited by aquasurf; 02-16-2021 at 12:24 AM.. Reason: additional information on hub centring rings
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